Evidence That Air Pollution May Shorten Lung Cancer Survival

Impact appears greatest among patients with early stage disease

Action Points

Note that this registry-based study of Californians with lung cancer found that exposure to air pollution was negatively associated with overall survival.

The association was particularly strong for those with early stage disease at diagnosis.

Exposure to air pollution following a diagnosis of lung cancer appears to be associated with shorter survival, according to findings from a population-based study from California.

When researchers examined air pollution exposures and outcomes among more than 350,000 residents of the state diagnosed with lung cancer between 1988 and 2009, they found shorter average and 5-year survival times among those with higher exposures to each of four measured air pollutants.

The trend was strongest among patients with early stage disease, particularly those with adenocarcinomas, wrote researcher Sandrah P. Eckel, PhD, of the University of Southern California in Los Angeles, and colleagues, in the study in Thorax, published online Aug. 4.

Eckel told MedPage Today that while the link between air pollution exposure and lung cancer incidence and mortality is fairly well established, the impact of exposure on survival after a lung cancer diagnosis has not been widely studied.

In 2013, air pollution was classified as carcinogenic by the World Health Organization's International Agency for Research on Cancer (IARC).

"We know that smoking is really the key risk factor for lung cancer, but we wanted to see if air pollution may be another modifiable risk factor for survival," Eckel said.

The study included all patients diagnosed with lung cancer in California over a 20-year period, identified through the California Cancer Registry.

Monthly average concentrations of the pollutants were spatially interpolated to the residence locations from as many as the four closest air quality monitoring stations within a radius of about 50 kilometers (~31 miles).

"Our primary goal was to evaluate associations with large-scale regional variation in ambient pollutants; so, to account for potential confounding by local traffic, we calculated and adjusted for the distance from residential address to primary interstate highway and primary U.S. and state highways," the researchers wrote.

Adjusted hazard ratios were smaller in later stages and varied by histological type within stage.

"Our observed associations were clinically significant (≤38% increased risk of death depending on stage and pollutant), suggesting that reductions in exposure have the potential to improve lung cancer survival," the researchers wrote. "As expected, we observed substantially larger association with survival in local compared with distant stage at diagnosis."

The strengths of the study included the comprehensive capture of lung cancers in California over a two-decade period and the high-quality monitoring of air quality in the state. Study limitations included the observational design and the lack of data on potentially confounding patient characteristics, including smoking status, behavioral changes, and change in residence after diagnosis.

While additional research is needed to validate and expand on the study findings, Eckel said the early research "brings into greater focus the potential importance of air pollution exposure on survival after a diagnosis of lung cancer."

"There are common sense things that patients can do to reduce their exposures, such as not exercising out of doors when air pollution levels are high, and closing windows during peak pollution times," she said.

In an editorial published with the study, Jaime E. Hart, ScD, of Brigham and Women's Hospital and Harvard Medical School in Boston, noted that while cancer survivorship has increased overall in recent decades, there has been only modest improvement in the survival rates for lung cancer.

Therefore, given the large impact of lung cancer and the relatively modest improvement in survival, "intervention strategies are appealing as a public health tool," she said.

"This emerging link between cancer survival and air pollution exposures should be seen as evidence of the importance of air pollution regulations, as well as a worthwhile target for interventions focused on increasing lung cancer survival rates."

This research was funded by among others, the Southern California Environmental Health Sciences Center and the National Institute of Environmental Health Sciences. The researchers disclosed having no relevant relationships with industry.

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